Conventionally, there has been known a technique for obtaining a polyester film for wrap-around labels that cause few troubles due to static electricity from a polyester with a low oligomer content without deteriorating the productivity and quality, by using a polyester resin obtained by recycling PET bottles (for example, see Patent Document 1). However, such a conventional technique is used for producing a film with low intrinsic viscosity (1V=0.62) using a raw material resin with high intrinsic viscosity (1V=0.70) by extrusion at a low extrusion temperature (280° C.), so that the composition of the inside of the film is uneven, which causes uneven lamination surface and unevenness in thickness. Further, in this technique, a film after biaxial stretching is subjected to a heat treatment at a high temperature in order to obtain high lamination strength. However, since the film is cooled to room temperature abruptly, there occur problems that relaxation of the film is nonuniform in the plane and that the unevenness in thickness is caused.
Further, there has been known a technique for controlling orientation of a film to provide a polyester film for transparent deposition suitable for adhesion of a deposited film to the polyester film and for boiling and retort treatment (for example, see Patent Document 2). However, such a conventional technique is an example of poly(ethylene terephthalate) that does not use a polyester resin obtained by recycling PET bottles, and in the case where a film is produced by using a resin same as the recycled resin and having an intrinsic viscosity of 0.63, the composition of the inside of the film is uneven, so that it results in generation of unevenness in a lamination surface or unevenness in thickness. Further, in this technique, a film after biaxial stretching is subjected to a heat treatment at a high temperature in order to obtain high lamination strength. However, since the film is cooled to room temperature abruptly, there occur problems that relaxation of the film is nonuniform in the plane and that the unevenness in thickness is caused.
Furthermore, there has been known a technique for making slitting property and cutting property in the calendering process good in a magnetic recording medium by controlling particles in a film and film production conditions (for example, see Patent Document 3). However, such a conventional technique is an example of poly(ethylene terephthalate) that does not use a polyester resin obtained by recycling PET bottles, and in the case where a film is produced by using a resin same as the recycled resin and having an intrinsic viscosity of 0.62, the composition of the inside of the film is uneven, so that it results in generation of unevenness in a lamination surface or unevenness in thickness. Further, in this technique, a film after biaxial stretching is subjected to a heat treatment at a high temperature in order to obtain high lamination strength. However, since the film is cooled to room temperature abruptly, there occur problems that relaxation of the film is nonuniform in the plane and that the unevenness in thickness is caused.
Still further, there has been known a technique for improving the heat dimensional stability at the time of producing a ceramic sheet to be used for a release sheet whose heat shrinkage is optimized by optimizing the lengthwise and transverse stretching condition and the heat treatment condition of the film (for example, see Patent Document 4). However, such a conventional technique is an example of poly(ethylene terephthalate) that does not use a polyester resin obtained by recycling PET bottles, and in the case where a film is produced by using a resin same as the recycled resin and having an intrinsic viscosity of 0.62, the composition of the inside of the film is uneven, so that it results in generation of unevenness in a lamination surface or unevenness in thickness. Moreover, there has been disclosed a technical idea of carrying out a heat treatment at a high temperature for a film after biaxial stretching and optionally carrying out cooling after the heat treatment to obtain high lamination strength. However, in the case of a film containing 0.5 mol % or more and 5 mol % or less of isophthalic acid, if this technique is employed as it is, relaxation of the film is nonuniform in the plane and the unevenness in thickness is caused. It is further disclosed that the refractive index (Nz) in the thickness direction is controlled to keep flatness of a film, but in this document, a case where poly(ethylene terephthalate) accounts for 100% and Nz is 1.493 or less is assumed. A film containing 0.5 mol % or more and 5 mol % or less of isophthalic acid is advantageous in that it easily provides sufficient lamination strength as compared with a poly(ethylene terephthalate) film containing 0 mol % of isophthalic acid, but its Nz is too high to improve lamination strength and reduce unevenness in thickness simultaneously. Accordingly, this technique cannot be employed as it is.